Biomimetic nanocluster photoreceptors for adaptative circular polarization vision

Nanoclusters with atomically precise structures and discrete energy levels are considered as nanoscale semiconductors for artificial intelligence. However, nanocluster electronic engineering and optoelectronic behavior have remained obscure and unexplored. Hence, we create nanocluster photoreceptors inspired by mantis shrimp visual systems to satisfy the needs of compact but multi-task vision hardware and explore the photo-induced electronic transport. Wafer-scale arrayed photoreceptors are constructed by a nanocluster-conjugated molecule heterostructure. Nanoclusters perform as an in-sensor charge reservoir to tune the conductance levels of artificial photoreceptors by a light valve mechanism. A ligand-assisted charge transfer process takes place at nanocluster interface and it features an integration of spectral-dependent visual adaptation and circular polarization recognition. This approach is further employed for developing concisely structured, multi-task, and compact artificial visual systems and provides valuable guidelines for nanocluster neuromorphic devices.

Supplementary Fig. 7 | Characteristics of pentacene film.(a) AFM image of pentacene deposited on Ag nanocluster film with a root-mean-square roughness of 6.82 nm.Scale bar: 1 μm.(b) AFM image of pentacene deposited on SiO2 with a root-meansquare roughness of 9.17 nm.Scale bar: 1 μm.Pentacene deposited on Ag nanoclusters displays lower roughness and reduced grain sizes compared to its analogue deposited directly on SiO2.(c) GIWAXS image of pentacene deposited on Ag nanocluster film.(d) GIWAXS image of pentacene deposited on SiO2.Lattice spacing and π-π stacking distances of pentacene films nearly remain consistent in two conditions.(e) XRD of the Ag nanocluster film, pentacene film deposited on Ag nanoclusters and pentacene film deposited on SiO2.Ag nanocluster film shows no diffraction peaks, while crystalline Supplementary Fig. 18  organic semiconductors, enabling more efficient charge transport at the ligand/organic semiconductor interface and potentially lower injection barrier.Meanwhile, the less 'conductive' alkyl chain would lead to electron tunneling rather than hopping that is readily available in aromatic ligands.Furthermore, we have proved our speculation by experiments and theoretical calculation.The alkyl ligand protected nanoclusters have notably inferior performance in memory capacity and retention time, being due to the following reasons: First, aromatic ligands function as a percolation pathway to transport charges, instead alkyl ligands break the coherence of π systems.Second, we find that two kinds of nanoclusters have slight difference in energy levels, which in turn governs the interfacial injection barrier or efficiency.The highest occupied molecule orbitals (HOMO) of nanoclusters are estimated from ultraviolet photoelectron spectroscopy (UPS) and the lowest un-occupied molecular orbitals (LUMO) are calculated from optical band gap, as shown in Supplementary Fig. 22 and Supplementary Table 1.Third, ligand-induced morphology evolution of nanoclusters.We find that the root-meansquare roughness of the alkyl ligand protected nanocluster film is 13.2 nm, being much higher than the aromatic one, which is responsible for non-uniformity, interfacial defect formation with high density and deteriorated performance.

S33
Supplementary of water, switching light absorption range to adapt to low-light environment 1,5,6 .

Circularly polarization vision:
Considering the microvillar structure of photoreceptor cells, R8 cell act as 1/4 wave plates with a fast axis parallel to their microvillar planes 7 .R8 cell enables to convert circularly polarized light into linearly polarized light, then processed by the R1-R7 cells.
In rows 5 and 6, because of an angle of 45° orientation of the R8 and R1-R7 microvillar planes, the R1-R7 cells suffice to distinguish clockwise-rotating and counterclockwiserotating electric vectors 8 .

Supplementary Note 5: In-sensor light valve charge reservoir model
Nanoclusters have many discrete energy levels, and electrons fill in the lower-energy orbitals, leaving many higher-energy empty orbitals.These empty orbitals can accommodate more electrons as well as photogenerated electrons.Since the electron clouds between nanoclusters cannot effectively overlap, we believe that the occupied levels in nanoclusters are independent.According to the definition of Fermi level in semiconductors, when the electron density in nanoclusters changes, the Fermi level will change accordingly.When nanoclusters contact semiconductors to form an interface, the Fermi levels of them always remain flat.Upon applying an electric field and light illumination to this interface, the gain and loss of electrons and holes between them are conserved.Initially, the density of electrons in nanoclusters and holes in channel is low.
After illumination, channel current increase indicates holes accumulation.Even after the light is removed, the current level is still higher than its initial value, which is a result of photo-generated electrons captured by nanoclusters.When electron and hole densities are prompted to a high level, channel current remains stable in the dark.Hence, | Electrical properties and morphology of quantum-dotinterfaced pentacene devices.(a) AFM of PbS dot film with a root-mean-square roughness (RRMS) of 4.34 nm.Scale bar: 400 nm.(b) AFM of carbon dot film with a RRMS of 0.248 nm.Scale bar: 1 μm.(c) Bidirectional transfer characteristics of PbS dots-based photoreceptors.(d) Bidirectional transfer characteristics of carbon dotsbased photoreceptors.These two types of devices show inferior photoperception capabilities.
Supplementary Fig. 22 | UPS and UV-vis spectra of nanocluster films.(a) UPS spectra of aromatic ligand protected nanoclusters.Inset, the enlarged image of UPS spectra.(b) UPS spectra of alkyl ligand protected nanocluster films.Inset, the enlarged image of UPS spectra.(c) UV-vis spectra of aromatic ligand protected nanoclusters.Inset, the enlarged image of UV-vis spectra.(d) UV-vis spectra of alkyl ligand protected nanocluster films.Inset, the enlarged image of UV-vis spectra.
nanoclusters have the ability to store and capture excess electrons.When light is shed, channel current decreases rapidly, indicating that light promotes the recombination of electrons and holes.Therefore, nanoclusters can be regarded as a reservoir, and light acts like a valve to switch the on and off of the reservoir.The in-sensor light valve charge reservoir model reveals nanocluster behaviors of charge storage, photogenerated exciton trapping and recombination.Each material has its unique characteristics, hence the light-valve model and charge reservoir model are not universal in all kinds of nanoclusters.In fact, we propose the light-valve model and charge reservoir model to account for the photoadaptation behavior.In our work, Ag nanoclusters are revealed with adaptative response to light, charge capture, and tunable Femi energy level, hence electronic states of Ag nanocluster can be synergistically tuned by gate bias and light.These characteristics are the prerequisite for the construction of nanocluster-type photoreceptors.To address your concern, there are four requirements to achieve a successful nanocluster/organic interface.First, nanoclusters should be composed of precious metal cores that offer plenty of empty orbitals for extra electrons and function as charge reservoir.Second, aromatic ligands are required to form effective hopping pathway for charge carrier transition to π-conjugated backbones of semiconductors.Third, nanoclusters should be synthesized with high absorption coefficient.Forth, π-conjugated backbone of semiconductors should be sterically adjacent to the ligands of nanoclusters to ensure effective charge transfer.In a control experiment, we use an interlayer of tetratetracontane (TTC) to physically isolate the nanocluster and the pentacene layer, leading to suppressed photoresponse in the device.According to these rules, not every and dispersed in toluene with a concentration of 25 mg mL −1 .Both of them were diluted to a concentration of 5 mg mL −1 .Parallel devices were fabricated with similar procedures in Ag nanocluster photoreceptors.As a result, these devices substituted by carbon dots and PbS dots demonstrate inferior optoelectronic performances under luminescence, as shown in Supplementary Fig.18.

Table 1 |
Summary of energy levels of Ag nanoclusters.
Supplementary Fig.30| CPL memory.After illumination of CPL (270 nm, 100 μW cm −2 ), current decay can be well fitted by exponential decay equation (3) given as following.Hence, the current of ACP tends to be stable after 100,000 s and remains at 1.2 µA and 1.3 µA for LCPL and RCPL, respectively.

Table 2 |
Comparison of the perception range (PR) and adaptation time (Tadapt) of adaptable ACP in this work with results in literature shown in Figure4e.